He used his maxed out lightspeed kick to bust Luffy through the robot and two explosive barriers, which did little to Luffy. He spammed clones equipped with Ama no Murakumo. He used lasers. Now his attacks don't seem to bother Luffy either.
Luffy using G5 against Kizaru really becomes irrelevant given he did the same against Lucci and literally made a circus show out of it. We also know Luffy used G4 against fodder, meaning wasting more energy than is necessary.
And since Haki has a higher ceiling, holding back on ACoC + ACoA is a bigger nerf than holding back on awakening, which Kizaru isn't even confirmed to have in the first place. The moment Luffy pulled out advanced Haki, we know how Kizaru looked like.